Pro-marijuana laws have led to significant decreases in violent crime in several U.S. states bordering Mexico, says a new study that was published in The Economic Journal. The study indicates that the rates of violent crime by drug trafficking organizations (DTOs) – including robberies, murders and aggravated assaults – have fallen by 12.5% in counties close to the border following the implementation of medical marijuana laws (MMLs).

Study author Professor Evelina Gavrilova said, “MMLs allow people to grow and cultivate marijuana plants legally within the US. This means that people don’t need to buy illegal marijuana anymore so drug trafficking organizations (DTOs) have far fewer customers,” according to the Independent UK.

The study says that, “Their namesake activity – the smuggling of illicit drugs – is known to be paired with extreme levels of violence, which DTOs use to contest the revenues in the drug market.”

Robberies have decreased by 19% in U.S. border states with legal medical marijuana programs, murders decreased by 10% and assaults reduced by 9%. The biggest decrease is for drug-law murders which decreased by 41%.

The marijuana market is the largest drug market in the U.S. It’s always been a “lucrative cash crop” for DTOs, according to the study. Most illegal drugs in the U.S. come through Mexico. Every year, roughly $6 billion goes back into Mexico to the DTOs.

Professor Gavrilova said, “It’s very likely that they are not going to simply give up on this market. There are reports that some DTOs are starting to grow their own opium, which could be used to produce heroin that is smuggled into the US. They could also enter the legal marijuana trade themselves by setting up farms in a border state.”